Mesoporous carbon molecular sieve and supported catalyst employing the same

ABSTRACT

The present invention is related to a mesoporous carbon molecular sieve, which can be used as a catalyst carrier capable of improving the activity of a supported catalyst and a method of preparing the same. Additionally, the invention is related to a supported catalyst employing the mesoporous carbon molecular sieve as a carrier, and a fuel cell employing the supported catalyst. The mesoporous carbon molecular sieve has an average primary particle size of less than about 500 nm, an average mesopore size in the range of about 3 nm to about 6 nm, and a surface area in the range of about 500 m 2 /g to about 2000 m 2 /g.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Patent Application No. 10/992,211filed on Nov. 19, 2004, now U.S. Pat. No. 7,220,697 which claims thebenefit of and priority from Korean Patent Application No. 2003-83041,filed on Nov. 21, 2003, in the Korean Intellectual Property Office, bothof which are incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention is related to a catalyst support, and inparticular, to a carbon-based catalyst support. In particular, thepresent invention is related to a supported catalyst employing thecarbon-based catalyst support. Also, the present invention is related toa fuel cell, and more particularly, to a fuel cell comprising thesupported catalyst employing the carbon-based catalyst support.

BACKGROUND

Fuel cells are inherently ultra-clean, highly reliable, and have highpower density and high energy-conversion efficiency. Also, since fuelcells can operate at an ambient temperature and can be fabricated inminiaturized form and hermetically sealed, they can be extensivelyapplied to power generating systems for home and regional use, medicalequipment, military equipment, space equipment, and used as powersources for portable electrical/electronic devices such as mobiletelecommunications equipment.

The fuel cell produces electricity through the electrochemical reactionof fuel, such as hydrogen, natural gas, and methanol, and an oxidizingagent. In general, the fuel cell consists of two electrodes—an anode anda cathode, which are sandwiched around an electrode membrane. The fuelis supplied to the anode where it is electrochemically oxidized, anoxidizing agent, such as oxygen or air, is fed to the cathode where itis electrochemically reduced, and the electrolyte membrane acts as apath for transporting ions produced at the anode to the cathode.Electrons generated at the anode by oxidation of the fuel go through anexternal circuit, creating a flow of electricity. The protons migratethrough the electrolyte to the cathode, where they reunite with theoxidization agent and the electrons to produce water and heat.

A catalyst contained in the anode and the cathode to promote theelectrochemical reactions is very important in the fuel cell having suchstructure. For example, in a polymer electrolyte membrane fuel cell(PEMFC) both of the anode and the cathode generally contain acarbon-supported platinum catalyst having platinum nanoparticlesdispersed in a microporous carbon support. Also, in a direct methanolfuel cell the anode catalyst may be, for example, a PtRu alloy powder ora carbon-supported PtRu catalyst having PtRu nanoparticles dispersed inthe microporous carbon support, and the cathode catalyst may be, forexample, a Pt particle powder or the carbon-supported platinum catalysthaving platinum nanoparticles dispersed in the microporous carbonsupport.

A catalyst support for a fuel cell must exhibit porosity to support anddisperse catalytic metal particles and electro-conductivity to act asthe path for the migration of electrons. In general, amorphousmicroporous carbon powder known as activated carbon or carbon black maybe used as a catalyst support for the fuel cell.

An amorphous microporous carbon powder is generally prepared bychemically and/or physically activating a raw material, such as wood,peat, charcoal, coal, brown coal, coconut peel, and petroleum coke, forexample. Generally, the activated carbon has pores exhibiting a diameterof less than about 1 nm and has a surface area of about 60 m²/g to about1000 m²/g. In particular, Vulcan Black and Kejten Black, which arecommercial products most broadly used as a catalyst support, have asurface area of about 230 m²/g and about 800 m²/g, respectively, andhave an average primary particle size of less than about 100 nm.Amorphous microporous carbon particles, however, have poor microporeinterconnection. Specifically, in a conventional DMFC, a supportedcatalyst using amorphous microporous carbon particles as a support haslower reactivity than a catalyst consisting of only metal particles.However, DMFCs employing metal particle catalysts are not cost effectivedue to the high costs associated with the metal particular catalysts.Thus, there is a need to develop a carbon-based catalyst support that iscapable of improving the reactivity of the catalyst for fuel cells, suchas PEMFCs, PAFCs and DMFC.

For example, the mesoporous carbon molecular sieve, disclosed in KoreanPatent Laid-Open Publication No. 2001-0001127 is an example of such acarbon-based catalyst support. This patent discloses a method ofpreparing an ordered mesoporous carbon molecular sieve using amesoporous silica molecular sieve, which is prepared using a surfactantas a template material. In this method based on nano-replication, theordered mesoporous silica molecular sieve, such as “MCM-48” and “SBA-1”,which has micropores connected three-dimensionally by mesopores is usedas a template to prepare an ordered mesoporous carbon molecular sieve,such as “CMK-1” and “CMK-2”, which has micropores and mesopores with auniform diameter and regularly arranged.

The mesoporous carbon molecular sieve prepared as described above may beused as a possible carbon-based catalyst support. However, since theparticle size of the mesoporous carbon molecular sieve is larger thanthose of Vulcan Black and Kejten Black, there is a need to improve thecatalytic activity in the mesoporous carbon molecular sieve.

SUMMARY OF THE INVENTION

The present invention is directed to an improved mesoporous carbonmolecular sieve and a method of preparing the same. The mesoporouscarbon molecular sieve of the invention may be used as a catalystsupport to improve the activity of a supported catalyst. Additionally,the present invention is also directed to a supported catalyst employingthe mesoporous carbon molecular sieve as a support. The presentinvention also provides a fuel cell employing the supported catalyst.

According to an aspect of the present invention, a mesoporous carbonmolecular sieve having an average primary particle size of less thanabout 500 nm, an average mesopore size in the range of about 3 nm toabout 6 nm, and a surface area in the range of about 500 m²/g to about2,000 m²/g is provided.

According to another aspect of the present invention, a method ofpreparing the mesoporous carbon molecular sieve is provided. Themolecular sieve may be prepared in the following manner. A mesoporoussilica molecular sieve having an average primary particle size in therange of about 100 nm to about 700 nm is prepared, then, the mesoporouscarbon molecular sieve using the mesoporous silica molecular sieve as atemplate is prepared.

An additional aspect of the present invention is directed to a method ofpreparing a mesoporous silica molecular sieve having an average primaryparticle size in the range of about 250 nm to about 700 nm. The silicamolecular sieve may be prepared in the following manger. A reaction ofSodium silicate with Na:Si having an atomic ratio of about 1.5 to about2.5, apoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol),and acetic acid in a water-based reaction medium may be employed toproduce precipitates, and then, the precipitates may be dried andcalcined.

According to another aspect of the present invention, a method ofpreparing the mesoporous carbon molecular sieve is provided. The methodmay be carried out in the following manner. A carbon precursor may befilled into pores of a template of the mesoporous silica molecular sievehaving an average primary particle size in the range of about 250 nm toabout 700 nm, then the carbon precursor may be thermally degraded byheating the template having the carbon precursor impregnated under anon-oxidizing atmosphere to form a carbon structure in the pores of thetemplate. Then, the template may be removed using a silica-solublesolution in order to isolate the carbon structure.

According to another aspect of the present invention, a supportedcatalyst including the mesoporous carbon molecular sieve having anaverage primary particle size of less than about 500 nm, an averagemesopore size in the range of about 3 nm to about 6 nm, and a surfacearea in the range of about 500 m²/g to about 2000 m²/g; and catalyticmetal particles dispersed in and supported on the mesoporous carbonmolecular sieve is provided.

According to another aspect of the present invention, a fuel cellcomprising a cathode, an anode, and an electrolyte membrane interposedbetween the cathode and the anode, where at least one of the cathode andthe anode may contain the supported catalyst according to the presentinvention is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an XRD analysis result for a mesoporous silicamolecular sieve obtained in an Example of the present invention.

FIG. 2 is a particle size distribution chart of a mesoporous carbonmolecular sieve according to an Example of the present invention.

FIG. 3 is a SEM photograph of a mesoporous carbon molecular sieveaccording to an Example of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a mesoporous carbon molecularsieve, which has the shape of a porous particle substantially consistingof carbon. Unlike a conventional amorphous microporous carbon powderhaving mainly micropores, the mesoporous carbon molecular sieve of thepresent invention may have both mesopores and micropores in anappropriate ratio. In the present invention, the term “micropores” meanspores having a diameter less than about 2 nm, the term “mesopores” meanspores having a diameter in the range of about 2 nm to about 10 nm, and amolecular sieve refers to porous particles having mesopores andmicropores with substantially uniform size.

In an embodiment of the present invention, pores of the mesoporouscarbon molecular sieve may or may not be regularly arranged. Regardlessof this, in the mesoporous carbon molecular sieve of the presentinvention, micropores interconnect via mesopores or mesoporesinterconnect via micropores. Accordingly, reactants can be easilysupplied, via mesopores, to micropores, and products created inmicropores can be easily discharged outside of supported catalystparticles through mesopores. Such a mesoporous carbon molecular sievemay be characterized by an average size (or diameter) of mesopores and asurface area as well as an average primary particle size.

When the mesoporous carbon molecular sieve is used as a support of asupported catalyst, as the primary particle size of the mesoporouscarbon molecular sieve decreases, electrochemical activity of thesupported catalyst increases compared with that of a conventional Blacksupported platinum catalyst. The diffusion of reactants and removal ofproducts in the supported catalyst may be smoothly performed bydecreasing the primary particle size of the mesoporous carbon molecularsieve having micropores and mesopores regularly arranged, thus enablingall of the catalytic metal particles present even in the micropores inthe support to participate in the electrochemical reaction.

There is an appropriate range for the average primary particle size ofthe mesoporous carbon molecular sieve used as the support, and theappropriate range is less than about 500 nm, and in particular, in therange of about 250 nm to about 350 nm. Specifically, the primaryparticle size may be about 300 nm.

The mesoporous carbon molecular sieve of the present invention may becharacterized as follows. The mesoporous carbon molecular sieve of thepresent invention may have an average mesopore size in the range ofabout 3 nm to about 6 nm and a surface area in the range of about 500m²/g to about 2000 m²/g. The average mesopore size of the mesoporouscarbon molecular sieve may be preferably in the range of about 3.5 nm toabout 5 nm. The surface area of the mesoporous carbon molecular sievemay be in the range of about 800 m²/g to about 1500 m²/g. A method ofpreparing the mesoporous carbon molecular sieve of the present inventionmay be performed as follows. A mesoporous silica molecular sieve havingan average primary particle size in the range of about 250 nm to about700 nm may be prepared, and then, a mesoporous carbon molecular sievemay be prepared by using the mesoporous silica molecular sieve as atemplate. In a further embodiment, the mesoporous silica may have anaverage primary particle size in the range of about 250 nm to about 500nm, and more specifically, in the range of about 275 nm to about 325 nm.The method of the present invention is based on “nano-replication”. Inother words, pores of the mesoporous silica molecular sieve used as thetemplate may be filled with carbon, and then the silica molecular sievemay be removed using a silica-soluble solution to isolate a carbonmolecular sieve. Here, the average primary particle size of the finalcarbon molecular sieve is proportional to the average primary particlesize of the mesoporous silica molecular sieve. Thus, the method mayinclude adjusting process of the particle size of the mesoporous silicamolecular sieve.

Additionally, the present invention may provide a method of adjustingthe average primary particle size of the mesoporous silica molecularsieve. The method may include reacting NaOH with SiO₂ in a water-basedreaction medium to form sodium silicate; reacting the sodium silicate, apoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol),and a pH controller in a water-based reaction medium to obtainprecipitates; and then, drying and calcining the precipitates to obtainthe mesoporous silica molecular sieve. The Na:Si atomic ratio of theformed sodium silicate may be adjusted by relatively adjusting theamounts of NaOH and SiO₂ when forming the sodium silicate, and theaverage particle size of the formed mesoporous silica may be decreasedby increasing the atomic ratio of Na:Si.

When forming sodium silicate, the water-based reaction medium acts as asolvent for NaOH and as a dispersion medium for SiO₂ particles. In orderto form sodium silicate having the desired Na:Si atomic ratio, NaOH andSiO₂ may be added to the water-based reaction medium in a relativeamount corresponding to the desired Na:Si atomic ratio. However, theabsolute contents of NaOH and SiO₂ are not particularly limited. Whenthe reactants are too diluted or concentrated, the reaction may notoccur smoothly. Therefore, the adding amount of NaOH may be typically inthe range of about 10 parts to about 30 parts by weight based on 100parts by weight of the water-based reaction medium. The added amount ofSiO₂ may be in the range of about 10 parts to about 15 parts by weightbased on 100 parts by weight of the water-based reaction medium. Thereaction temperature and the reaction time in this step are notparticularly limited. When the reaction temperature is too low, SiO₂ maynot dissolve well. When the reaction temperature is too high, thecomposition of the whole solution may fluctuate. Therefore, the reactiontemperature may be in the range of about 60° C. to about 80° C. Thereaction time may be easily selected to obtain sodium silicate at anappropriate yield according to other reaction conditions and istypically in the range of about 0.5 hours to about 2 hours. Theresultant product may be a type of transparent water-based solutioncontaining sodium silicate.

Next, the sodium silicate, thepoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol),and the pH controller may be reacted in a water-based reaction medium toobtain precipitates. In this step, the sodium silicate may be added tothe water-based reaction medium in a dried state or in the form of thetransparent water-based solution obtained in the previous step. Thepoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol)(P123 polymer (BASF Co.)) may be used as a template material to formmicropores. As the pH controller, a general acid may be used. Arepresentative example of the pH controller may be acetic acid.

When the amount of sodium silicate added to the water-based reactionmedium is too low, the mesoporous structure may not form. When theamount of sodium silicate is too high, the amount of amorphous SiO₂ mayincrease. Therefore, the amount of sodium silicate added to thewater-based reaction medium may be in the range of about 13 parts toabout 20 parts by weight based on 100 parts by weight of the water-basedreaction medium.

When the amount ofpoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol)added to the water-based reaction medium is too little, mesopores maynot form. When the amount ofpoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol)is too great, a mesoporous substance of non-desirable structures mayform or no structure may form. Therefore, the amount ofpoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol)added to the water-based reaction medium may be in the range of about 1part to about 5 parts by weight based on 100 parts by weight of thewater-based reaction medium.

Also, if the amount of acetic acid added to the water-based reactionmedium is too little, a large amount of NaOH may not be neutralized, andthe structure formation cannot be performed. When the amount of theacetic acid added to the water-based reaction medium is too great, theacidity increases, and the particle size of silica substance cannot becontrolled. Hence, the amount of acetic acid added to the water-basedreaction medium may be in the range of about 2 parts to about 7 parts byweight based on 100 parts by weight of the water-based reaction medium.

The order of adding the reactants to the water-based reaction medium isnot particularly limited. Typically, the transparent water-basedsolution containing sodium silicate may be mixed with an aqueouspoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol)solution, and then the acetic acid may be added to the mixture. In thisstep, the reaction temperature and the reaction time are notparticularly limited. However, when the reaction temperature is too low,thepoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol)may not dissolve well in the water-based reaction medium. When thereaction temperature is too high, the composition of the solution or thestructure of the silica substance may fluctuate. Therefore, the reactiontemperature is typically in the range of about 30° C. to about 60° C.The reaction time may be easily selected to obtain precipitates at anappropriate yield, according to other reaction conditions, and istypically in the range of about 5 hours to about 48 hours. The resultantprecipitates are a type of white powder.

The resultant precipitates are separated and dried and then subjected tocalcination to obtain the mesoporous silica molecular sieve having thedesired average primary particle size. The separation of precipitatesmay be performed in a conventional manner, such as filtration/washing,and centrifuging. The drying temperature and drying time of theprecipitates are not particularly limited. Typically, drying of theprecipitates may be performed at room temperature for a time period inthe range of about 12 hours to about 36 hours. Then, the driedprecipitates may be calcined. The calcination may be performed under anoxidizing atmosphere such as air. When the calcination temperature istoo low, micropores are not created since the template material andother impurities remain. When the calcination temperature is too high,the uniformity of the micropores may decrease. Therefore, thecalcination temperature may be in the range of about 450° C. to about700° C. Also, when the calcination time is too short, the templatematerial and other impurities can possibly remain. When the calcinationtime is too long, a large amount of time may be spent to calcine. Inview of this, the calcination time may be in the range of about 5 hoursto about 15 hours.

In order to adjust the average primary particle size of the silicamolecular sieve to the range of about 250 nm to about 700 nm, the Na:Siatomic ratio of sodium silicate may be adjusted to about 1.5 to about2.5. Accordingly, the method of preparing the mesoporous silicamolecular sieve having the average primary particle size in the range ofabout 250 nm to about 700 nm includes reacting sodium silicate withNa:Si atomic ratio of about 1.5 to about 2.5, thepoly(ethyleneglycol)-block-poly(propyleneglycol)-block-poly(ethyleneglycol),and acetic acid to obtain precipitates; and drying and calcining theprecipitates.

As described above, the mesoporous carbon molecular sieve of the presentinvention may be prepared using nano-replication. In other words, themethod of preparing the mesoporous carbon molecular sieve may includefilling a carbon precursor into pores of a template composed of themesoporous silica molecular sieve having an average primary particlesize in the range of about 250 nm to about 700 nm; thermally decomposingthe carbon precursor by heating the template having the carbon precursorimpregnated under non-oxidizing atmosphere, to form a carbon structurein the pores of the template; and removing the template using asilica-soluble solution to isolate the carbon structure.

The mesoporous silica molecular sieve having an average primary particlesize of about 250 nm to about 700 nm as described above may be used asthe template for the nano-replication. The carbon precursor filled inthe pores of the template may be any material capable of beingcarbonized by thermal decomposition. Examples of the carbon precursorinclude a polymer of a carbon-containing compound capable of beingpolymerized. The polymerization includes various types ofpolymerization, such as addition polymerization and condensationpolymerization, for example. Examples of the carbon-containing compoundcapable of being polymerized include carbohydrates and monomers, forexample. Hereinafter, the carbon-containing compound capable of beingpolymerized is referred to as a polymerizable carbon-containingcompound.

The carbohydrates are classified into monosaccharides, oligosaccharides,and polysaccharides. In the present invention, monosaccharides,oligosaccharides, and a mixture thereof may specifically be used.Representative examples of the monosaccharides include glucose,fructose, mannose, galactose, ribose, and xylose. These materials may beused alone or in a combination of two or more. The oligosaccharides arecarbohydrates composed of two or more of monosaccharides joined togetherby a glycoside link. Saccharides from disaccharides composed of twomonosaccharides to decasaccharides composed of ten monosaccharides arecollectively called oligosaccharides. The oligosaccharides may includesimple ones, which are composed of one type of monosaccharide, andcomplicated ones, which may be composed of two or more types ofmonosaccharides. Of the oligosaccharides, disaccharides are mainlypresent in the natural world in an isolated state. Specific examples ofthe disaccharides include sucrose contained in sugar canes, maltose(malt sugar) which is a digested material of starch by amylase and is araw material of wheat gluten, lactose (milk sugar) contained in the milkof mammals, and the like. Reducing groups of these saccharides andhydroxy groups of saccharides or compounds except for the saccharidesmay undergo dehydration condensation.

Representative examples of a monomer that can be used as thepolymerizable carbon-containing compound include furfuryl alcohol,divinylbenzene, phenol-formaldehyde, resorcinol-formaldehyde and thelike.

The method of filling the carbon precursor in the pores of the templatemay be carried out as follows. First, a mixture containing thepolymerizable carbon-containing compound and a liquid carrier may beimpregnated into the pores of the template. Then, the polymerizablecarbon-containing compound may be polymerized in the template to form apolymer of the polymerizable carbon-containing compound in the pores ofthe template. These processes may be repeated one or two times or more.

The carrier is in a liquid state and acts as a solvent dissolving thepolymerizable carbon-containing compound and as a medium carrying thepolymerizable carbon-containing compound to the pores of the template.The carrier may be selected from, for example, water, an organicsolvent, and a mixture thereof. In particular, the organic solvent maybe alcohol. More particularly, the alcohol may be ethanol. Furfurylalcohol may be used as the polymerizable carbon-containing compound oras the carrier. Furfuryl alcohol used as the polymerizablecarbon-containing compound may also be the carrier.

The mixture may further comprise an acid. The acid may promote thepolymerization of the carbon precursor. The acid may be selected from,for example, sulphuric acid, hydrochloric acid, nitric acid, sulfonicacid, derivatives thereof, and a mixture of two or more of the foregoingmaterials. Representative examples of the sulfonic acid may includemethylsulfonic acid and the like.

The concentrations of the respective constituents in the mixture are notparticularly limited provided that the purpose of the present inventioncan be accomplished. For example, the concentrations of the respectiveconstituents in the mixture may be as follows.

When the concentration of the carrier is too low, impregnation of themixture into the template may not be easily performed. When theconcentration of the carrier is too high, the amount of carbon filled inthe template may be excessively decreased. Therefore, the concentrationof the carrier may be, for example, in the range of about 300 parts toabout 1000 parts by weight based on 100 parts by weight of thepolymerizable carbon-containing compound.

When the concentration of the acid is too low, the effect of promotingthe polymerization of the polymerizable carbon-containing compoundaccording to the addition of an acid may be trivial. When theconcentration of the acid is too high, the catalyzing effect may besaturated. In view of this, the concentration of the acid may be, forexample, in the range of about 1 part to about 30 parts by weight basedon 100 parts by weight of the polymerizable carbon-containing compound.

The polymerization of the polymerizable carbon-containing compound inpores of the template may be performed by, for example, heating, UVirradiation, and the like. When polymerizing by heating, a heatingtemperature too low may result in insufficient polymerization and aheating temperature too high may decrease the uniformity of theresulting carbon molecular sieve. In view of this, the heatingtemperature of the template having the mixture impregnated therein maybe, for example, in the range of about 50° C. to about 250° C.Alternatively, the heating may be performed in two steps of a firstheating and a second heating. For example, the first heating may beperformed at a temperature of about 50° C. to about 150° C. and thesecond heating may be performed at a temperature of about 150° C. toabout 250° C. Through these heating processes, the carbon precursor canbe polymerized and the liquid carrier can be vaporized.

Thus, the carbon precursor, i.e., the polymer of the polymerizablecarbon-containing compound, filled in the template is converted to thecarbon structure via thermal decomposition. In other words, the carbonprecursor filled in pores of the template is carbonized by thermaldecomposition. The thermal decomposition may be performed, for example,by heating the template having the carbon precursor impregnated thereinat a temperature in the range of about 400° C. to about 1400° C. under anon-oxidizing atmosphere. The non-oxidizing atmosphere may be selectedfrom among a vacuum, a nitrogen atmosphere, and inactive gasatmospheres. During this process, the carbon precursor is carbonized andthe carrier and/or acid are removed via evaporation or decomposition.

After converting the carbon precursor filled in the template to thecarbon structure, the template which is a silica molecular sieve may beremoved by treating it with a solution capable of selectively dissolvingsilica. Examples of the solution capable of selectively dissolving onlysilica include an aqueous hydrofluoric acid solution, an aqueous sodiumhydroxide solution, and the like. It is known that silica may beconverted to a soluble silicate by alkaline fusion or carbonate meltingand reacted with HF to form erodible SiF₄. The template may be treatedwith the silica-soluble solution several times depending on the type ofsilica molecular sieve used as the template so as to remove thetemplate. Also, ethanol may be further added to the solution. Due toremoval of the template, the carbon molecular sieve can be separatedfrom the pores of the template.

The supported catalyst of the present invention may comprise themesoporous carbon molecular sieve having mesopores with an average sizeof about 250 nm and a maximum particle size of about 500 nm, microporeswith an average size in the range of about 3 nm to about 6 nm, a surfacearea in the range of about 500 m²/g to about 2000 m²/g; and catalyticmetal particles dispersed in and supported on the carbon molecularsieve.

In the supported catalyst of the present invention, the mesoporouscarbon molecular sieve of the present invention as described above maybe used as a support, and the catalytic metal particles may be dispersedin pores of the support.

As described above, when the mesoporous carbon molecular sieve may beused as the support of the supported catalyst, as the primary particlesize of the mesoporous carbon molecular sieve decreases, electrochemicalactivity of the supported catalyst increases. By reducing the primaryparticle size of the mesoporous carbon molecular sieve having regularlyarranged micropores and mesopores, the diffusion of reactants and theremoval of products in the supported catalyst can occur smoothly, thusenabling all of the catalytic metal particles even in the micropores ofthe support to participate in the electrochemical reaction. However,when the primary particle size of the mesoporous carbon molecular sieveis too small, particles of the supported catalyst seriously agglomerate,thereby rather decreasing the coefficient of catalyst utilization. Thereis an appropriate range for the average primary particle size of themesoporous carbon molecular sieve used as the carrier, and theappropriate range is less than about 500 nm, and more specifically inthe range of about 250 nm to about 350 nm, and more specifically about300 nm. The supported catalyst of the present invention has improvedcatalytic activity by using the support having an average primaryparticle size within the above range.

The catalytic metal that can be used for the supported catalyst of thepresent invention is not particularly limited and examples thereofinclude titanium (Ti), vanadium (V), chrome (Cr), manganese (Mn), iron(Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), aluminium (Al),molybdenum (Mo), selenium (Se), tin (Sn), platinum (Pt), ruthenium (Ru),palladium (Pd), tungsten (W), iridium (Ir), osmium (Os), rhodium (Rh),niobium (Nb), tantalum (Ta), lead (Pb), and a mixture of two or more ofthe foregoing metals.

The catalytic metal may be appropriately selected depending on aspecific reaction to which the supported catalyst is to be applied.Also, the catalytic metal may be a single metal or an alloy of two ormore metals.

Specifically, when the supported catalyst of the present invention isused for a catalyst layer of a cathode or an anode of a fuel cell suchas PAFC, PEMFC, or the like, Pt may be generally used as the catalyticmetal. Further, when the supported catalyst of the present invention isused for a catalyst layer of an anode of DMFC, a Pt—Ru alloy may begenerally used as the catalytic metal. In this case, the atomic ratio ofPt—Ru may be typically about 0.5:1 to about 2:1. Further, when thesupported catalyst of the present invention is used for a catalyst layerof a cathode of DMFC, Pt may be generally used as the catalytic metal.

When the average particle size of the catalytic metal particles is toosmall, the catalyst may not catalyse the catalytic reaction. When theaverage particle size of the catalytic metal particles is too large, areaction surface area is decreased, resulting in reduced catalyticactivity. In view of this, the average particle size of the catalyticmetal particles may be in range of about 1 nm to about 5 nm.

When the concentration of catalytic metal particles in the supportedcatalyst is too low, the catalyst cannot be applied to a fuel cell, andwhen the concentration of catalytic metal particles in the supportedcatalyst is too high, the catalyst particle size can increase. In viewof this, the concentration of catalytic metal particles in the supportedcatalyst may be in the range of about 50% to about 80% by weight basedon the total weight of the supported catalyst.

To prepare the supported catalyst of the present invention, variousknown methods of preparing a supported catalyst can be used. Forexample, the supported catalyst of the present invention can be preparedby impregnating a solution of the catalytic metal precursor in thecarrier and then by reducing the catalytic metal precursor.

The fuel cell of the present invention may comprise a cathode, an anode,and an electrolyte membrane interposed between the cathode and theanode, and at least one of the cathode and the anode contains thesupported catalyst of the present invention. Examples of the fuel cellof the present invention include PAFC, PEMFC, or DMFC. The constructionof the fuel cells and the method of manufacturing such fuel cells, arenot particularly limited, and specific examples thereof are known invarious literatures in detail, and thus the detailed description thereonwill not be provided here.

EXAMPLES Specific Examples 1-2 Preparation of a Solution of SodiumSilicate

To control the average primary particle size of the mesoporous silicamolecular sieve, sodium silicate solutions with different Na:Si atomicratios were prepared. Na:Si atomic ratios of sodium silicate in thesodium silicate solutions prepared in Examples 1-2 were 1.5:1 and 2.5:1,respectively.

To prepare sodium silicate solutions of Examples 1-2, the correspondingamount of NaOH was first dissolved in distilled water, and then, LudoxHS-40 (Dupont, USA; the content of SiO₂:40% by weight) was added theretowhile stirring. The, contents of SiO₂ added to each of the solutionswere identically 10% by weight. Then, the mixture was heated at atemperature of about 75° C. for about 30 minutes to obtain a clearsolution. The conditions for preparing the sodium silicate solutions ofExamples 1-2 are summarized in Table 1 below.

TABLE 1 Na:Si atomic ratio of Amount of Amount of Amount of generatedwater (g) NaOH (g) Ludox HS-40 sodium used used (g) used silicatePreparation 413.8 49.9 125 1.5 Example 1 Preparation 406.3 83.2 125 2.5Example 2

Specific Examples 3-4 Preparation of a Mesoporous Silica Molecular Sieve

To prepare the mesoporous silica molecular sieves of Examples 3-4, P123polymer was dissolved in distilled water and sodium silicate solutionsof Examples 1-2, respectively, were added to the resulting solutionwhile stirring. An acetic acid was added to the mixture and heated atabout 45° C. for about 24 hours to produce precipitates. Theprecipitates were filtered and washed with distilled water and thendried in a vacuum oven at room temperature for about 24 hours. The driedprecipitates were calcined at about 550° C. for about 10 hours. Theconditions for preparing the mesoporous silica molecular sieves ofExamples 3-4, respectively, are summarized in Table 2 below.

TABLE 2 Sodium silicate solution Average primary Amount Amount Na:Siatomic particle size of of water of P123 Solution Amount ratio of sodiumAmount of acetic resulting silica (g) used (g) used used (g) usedsilicate acid (g) used molecular sieve (nm) Specific 59.9 1.643Preparation 10 1.5 1.498 700 Example 3 Example 1 Specific 59.9 1.643Preparation 10 2.5 2.496 300 Example 3 Example 2

FIG. 1 is an XRD analysis result for the mesoporous silica molecularsieves of Examples 3-4. Referring to FIG. 1, it is apparent from a peakshown around 2θ and the weaker peaks shown thereafter, that themesoporous silica molecular sieves of Examples 3-4 were well-ordered.The particle size of each of the mesoporous silica molecular sieves ofExamples 3-4 was measured from its SEM photograph, and the result isshown in Table 2.

Specific Examples 5-6 Preparation of a Mesoporous Carbon Molecular Sieve

The mesoporous carbon molecular sieve of Example 5 was prepared usingthe mesoporous silica molecular sieve obtained in Example 3 as atemplate.

0.94 g of sucrose was dissolved in 3.75 g of secondary distilled water,and 0.11 g of 97% sulphuric acid was added to the aqueous solution toprepare a polymerizable carbon-containing compound impregnatingsolution. The impregnating solution was supported on the mesoporoussilica molecular sieve obtained in Example 3 using an impregnatingmethod. The impregnated silica molecular sieve was dried at about 100°C. for about 6 hours and heated at about 160° C. for 6 hours again. Thesilica molecular sieve that had undergone the first impregnation anddrying, was impregnated again in the polymerizable carbon-containingcompound impregnating solution, and then the resultant was dried andheated in the same manner as above. The amount of the impregnatingsolution used at the time of the second impregnation was about 60% ofthe amount of the impregnating solution used at the time of the firstimpregnation. The silica molecular sieve which had undergone the secondimpregnation and drying, was heated under a nitrogen atmosphere at about200° C. for about 2 hours and then at about 900° C. for about 2 hours tocarbonize the polymer from sucrose in the silica molecular sieve.

The silica molecular sieve having the carbonized sucrose polymer wasadded to a solution of HF/H₂O/EtOH mixture (10% by weight of HF, 10% byweight of H₂O, and 80% by weight of EtOH). The mixture was stirred atroom temperature for about 2 hours, and the silica molecular sieve wasdissolved, allowing a carbon structure formed in the silica molecularsieve template to be isolated. The carbon materials (mesoporous carbonmolecular sieve) was filtered and washed three times with seconddistilled water. These dissolving-filtering-washing processes werefurther performed two times to obtain a final carbon structure, whichwas dried at about 100° C. for about 12 hours.

Mesoporous carbon molecular sieve of Examples 2-6 was prepared in thesame manner as in Example 5, except that the mesoporous silica molecularsieves of Example 4 were used as the template.

The physical properties of the mesoporous carbon molecular sieves ofExample 5 and Example 6 are summarized in Table 3 below.

TABLE 3 Example 5 Example 6 Size of template (nm) 300 700 used Physicalproperties of prepared mesoporous carbon molecular sieve Average primary298 552 particle size (nm) Average size of 3.9 3.7 mesopore (nm) Surfacearea (m²/g) 1158 1510

FIG. 2 is a particle size distribution chart of the mesoporous carbonmolecular sieve of Example 2. Referring to FIG. 2, the average primaryparticle size of the mesoporous carbon molecular sieve of Example 5 is298 nm and the maximum particle size of the mesoporous carbon molecularsieve of Example 5 is about 500 nm. FIG. 3 is an SEM photograph of themesoporous carbon molecular sieve of Example 5. Referring to FIG. 3, themesoporous carbon molecular sieve powder according to Example 5 iscomposed of spherical particles having a very uniform size.

Specific Examples 7-8 Preparation of a Supported Catalyst

The supported catalyst of Example 7 is a carbon supported platinumcatalyst using the mesoporous carbon molecular sieve obtained in Example5 as a support. The supported catalyst was prepared as follows.

0.5 g of the mesoporous carbon molecular sieve was mixed with a solutionof 0.9616 g of H₂PtCl₆ in 1.5 ml of acetone and the mixture was dried inthe air for about 4 hours. The mesoporous carbon molecular sieve havingan impregnated platinum precursor was placed in a crucible and dried atabout 60° C. for more than about 12 hours. After placing the crucible inan electric furnace, nitrogen gas was supplied to the furnace for about10 minutes, and then the atmosphere of the electric furnace was switchedto hydrogen gas, thereby reducing the platinum precursor. This heatingprocess was performed once again, and the carbon supported platinumcatalyst with platinum loading amount of about 60% by weight wasprepared.

The carbon supported platinum catalysts of Example 8 was prepared in thesame manner as in Example 7, except that the mesoporous carbon molecularsieve of Example 6 was used as carriers.

Specific Examples 9-10 Manufacturing of a Fuel Cell

The fuel cell of Example 9 included a cathode containing the supportedcatalyst of Example 7, an anode containing a PtRu black catalyst, and aNafion 117 electrolyte membrane. The loading of platinum in the cathodewas 3 mg/cm², and the loading of PtRu in the anode was 8 mg/cm².

The fuel cell of Example 10 was manufactured in the same manner as inExample 9, except that the carbon supported platinum catalyst of Example8 was used in the cathode.

The fuel cell of Example 11 was manufactured in the same manner as inExample 10, except that the conventional carbon black supported platinumcatalyst was used in the cathode.

Evaluation of Performance of the Fuel Cell

The performance of each of the fuel cells of Example 9 and Examples 10and 11 was measured under the following conditions. A 2M aqueousmethanol solution was used as a fuel, and air was used as an oxidizingagent. The working temperature of the fuel cells was 40° C. Theevaluation results of the performance are summarized in Table 4 below.

TABLE 4 Example 11 Example 9 Example 10 (Pt/black) Current density 42 8160 (mA/cm²) @ 0.4 V, 40° C. Particle size of Pt 2.8 3.1 8.0 catalyst(nm)

As is apparent from Table 4, the fuel cell of Example 10 has much highercurrent density generated at 0.4 V of potential than the fuel cells ofExamples 10 and 11. In other words, the mesoporous carbon molecularsieve of the present invention can greatly improve the electrochemicalactivity of the fuel cell.

However, comparing the fuel cells of Examples 10 and 11, it can be seenthat the performance of a fuel cell is not necessarily improved by usingthe mesoporous carbon molecular sieve. Since the catalyst particle sizeof Example 8 is much less than that of Pt Black catalyst, the fuel cellof Example 10 using the catalyst of Example 8 must have higherperformance than the fuel cell of Example 11 using the Pt Blackcatalyst. However, the performance of the fuel cell of Example 11 isindeed higher than the fuel cell of Example 10. This is because theaverage primary particle size of the support of 550 nm is too large toutilize all catalyst particles dispersed in the support. Moreover, thecatalyst of Example 8 prepared using the mesoporous carbon molecularsieve of Example 5 with the particle size distribution illustrated inFIG. 2 as a support has the primary particle size of the supportsufficient to utilize catalyst particles. Thus, the fuel cell of Example10 using the catalyst of Example 8 has the improved performance.

When the mesoporous carbon molecular sieve of the present invention,having an average primary particle size of 500 nm and less, is used as acarrier of a supported catalyst, the diffusion of reactants and theremoval of products in the supported catalyst occur and the support canparticipate in the electrochemical reaction. Accordingly, the supportedcatalyst of the present invention can display improved catalyticactivity by using the above support. Also, the fuel cell using thesupported catalyst of the present invention can display improvedelectrochemical activity.

1. A supported catalyst, comprising: a mesoporous carbon molecular sievehaving an average primary particle size of less than about 500 nm, anaverage mesopore size in the range of about 3 nm to about 6 nm, and asurface area in the range of about 500 m²/g to about 2000 m²/g; andcatalytic metal particles dispersed in and supported on the mesoporouscarbon molecular sieve.
 2. The supported catalyst of claim 1, whereinthe mesoporous carbon molecular sieve has an average primary particlesize in the range of about 250 nm to about 350 nm.
 3. The supportedcatalyst of claim 1, wherein the mesoporous carbon molecular sieve has asurface area in the range of about 1000 m²/g to about 1500 m²/g.
 4. Afuel cell comprising a cathode, an anode, and an electrolyte membraneinterposed between the cathode and the anode, wherein at least one ofthe cathode and the anode contains a supported catalyst comprising: amesoporous carbon molecular sieve having an average primary particlesize of less than about 500 nm, an average mesopore size in the range ofabout 3 nm to about 6 nm, and a surface area in the range of about 500m²/g to about 2000 m²/g; and catalytic metal particles dispersed in andsupported on the mesoporous carbon molecular sieve.
 5. The fuel cell ofclaim 4, wherein the mesoporous carbon molecular sieve has an averageprimary particle size in the range of about 250 nm to about 350 nm. 6.The fuel cell of claim 4, wherein the mesoporous carbon molecular sievehas a surface area in the range of about 1000 m²/g to about 1500 m²/g.